1. Field of the Invention
The invention relates to a communications network and, more particularly, to a method for data transmission in a local area network and a corresponding network.
2. Description of the Related Art
For many applications, local area networks have to fulfil certain requirements with respect to a data transmission in the network. For example, in wireless factory automation sensor systems in which the local area network comprises sensor nodes and a base station collecting data from the sensor nodes, cyclic data traffic characteristics have to be kept with respect to low latency and packet loss rates.
To fulfil these requirements, certain mechanisms for a data transmission are provided in the L2 or Media Access Control (MAC) layer of the well-known Open System Interconnection (OSI) reference model.
In the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard defining the MAC layer for data transmissions in wireless sensor networks, the use of acknowledgements for confirming a successful data transmission is described. After a data transmission, the sender and receiver switch the sending direction and the receiver sends an acknowledgement when the data was received correctly. If an acknowledgement is not received by the sender within a certain time interval, it can attempt to retransmit the data. Ghulam et al., “Extending the MAC Superframe of 802.15.4” Spec, August 2008 (“Ghulam”), referring to the aforementioned standard, proposes a MAC frame structure including acknowledgements and time slots reserved for retransmission of data not transmitted successfully. According to the time frame structure in this publication by Ghulam, many time-consuming changes between the transmission directions within a time frame are performed during data transmission.
Bahr M. et al.: Proposal for Factory Automation, September 2008, (“Bahr”) discloses a proposal for IEEE standard 802.15.4e being an extension of IEEE standard 802.15.4 designed for sensor networks usable in factory automation environments.
The Bahr document describes the transmission of group acknowledgements for acknowledging a number of transmissions within a single acknowledgment. This group acknowledgement is included in a beacon that is a synchronising message at the beginning of a time frame. The Bahr document, however, does not describe a mechanism for retransmitting lost data.